In a crystalline polymer of the polyolefin resin such as polyethylene, polypropylene or polybutene-1, there were problems such as its long molding cycle due to its slow crystallization rate after heat molding. In addition, there were some cases where molded articles altered their shape because crystallization proceeded even after the molding. Also, since these crystalline polymers generate large crystals when subjected to the heat molding, there were drawbacks in that the strength of the molded article are not sufficient and its transparency are poor.
These drawbacks are originated from the crystalline ability of the crystalline polymer. It has been known that the drawbacks can be solved by rapidly generating fine crystals. Currently, in order to rapidly generate the fine crystals, a method of adding a nucleating agent, crystallization promoting agent or the like is employed, in addition to a method of rising a crystallization temperature.
Examples of the above-mentioned nucleating agent or crystallization promoting agent include carboxylic acid metal salts such as sodium benzoate, aluminum 4-tertiary butyl benzoate salts or sodium adipic acid; phosphate metal salts such as sodium bis(4-tertiary butyl phenyl)phosphate or sodium 2,2′-methylenebis (4,6-di-tertiary butyl phenyl)phosphate; and compounds such as polyalcohol derivatives (e.g. dibenzylidene sorbitol, bis(methyl benzylidene)sorbitol or bis(dimethyl benzylidene)sorbitol). These nucleating agents and crystallization promoting agents are disclosed, for example, in Patent Documents 1 to 9.
In addition, Patent Documents 10 to 14 report a combined use of a nucleating agent made of a phosphate metal salt and an aliphatic organic acid metal salt. Further, Patent Document 15 reports a nucleating agent made of a phosphate metal salt having an average diameter of the longer axis of not more than 10 μm, an average aspect ratio of not more than 10 and a bulk specific gravity of not less than 0.1. Furthermore, as means for improving the transparency of crystalline resin, a technique using a nucleating agent and petroleum resin in combination has been known, which is reported, for example, in Patent Documents 16 to 19.
Further, in a sole addition of the nucleating agent to resin, there are problems such as working environment accompanying an addition of powders; as well as a problem of handling ability such as blocking by secondary aggregation of the nucleating agent. Due to this, the nucleating agent has been made into a masterbatch and, for example, Patent Documents 20 and 21 report masterbatches for polyolefin resin.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 58-1736
Patent Document 2: Japanese Unexamined Patent Application Publication No. 59-184252
Patent Document 3: Japanese Unexamined Patent Application Publication No. 6-340786
Patent Document 4: Japanese Unexamined Patent Application Publication No. 7-11075
Patent Document 5: Japanese Unexamined Patent Application Publication No. 7-48473
Patent Document 6: Japanese Unexamined Patent Application Publication No. 8-3364
Patent Document 7: Japanese Unexamined Patent Application Publication No. 9-118776
Patent Document 8: Japanese Unexamined Patent Application Publication No. 10-25295
Patent Document 9: WO 99/18108 pamphlet
Patent Document 10: Japanese Patent No. 3046428
Patent Document 11: Japanese Patent No. 3058487
Patent Document 12: Japanese Unexamined Patent Application Publication No. 5-43746
Patent Document 13: Japanese Unexamined Patent Application Publication No. 8-134260
Patent Document 14: Japanese Unexamined Patent Application Publication No. 8-120116
Patent Document 15: Japanese Unexamined Patent Application Publication No. 2001-59040
Patent Document 16: Japanese Unexamined Patent Application Publication No. 58-25431
Patent Document 17: Japanese Patent No. 2111515
Patent Document 18: Japanese Patent No. 2641180
Patent Document 19: Japanese Patent No. 3337261
Patent Document 20: Japanese Unexamined Patent Application Publication No. 9-157437
Patent Document 21: Japanese Unexamined Patent Application Publication No. 2000-003658